This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Gene Chemical Nature”.
1. The DNA structure was investigated in the year __________
Explanation: The structure of DNA was investigated and elucidated in the year 1953 by James Watson and Francis Crick at Cambridge University.
2. Nucleotide, basic unit of DNA consists of the sugar _________________
Explanation: Nucleotide consists of five-carbon sugar deoxyribose to which one phosphate is esterified at the 5’ position of the sugar ring and one nitrogenous base is attached at 1’.
3. Purines are a type of nitrogenous bases that consist of _____ ring(s).
Explanation: In a nucleotide, nitrogenous base is attached at the 1’ site. There are two types of nitrogenous base: pyrimidines, which consist of one ring, and purines, which contain two rings.
4. Guanine and adenine are _______________
Explanation: Purines are nitrogenous bases consisting of two rings. Adenine and guanine are purines whereas thymine and cytosine are pyrimidines.
5. A nucleotide has a non-polarized structure.
Explanation: A nucleotide has a polarized structure: the end where phosphate is attached is called the 5’end while the other is called 3’ end. All the stacked nucleotides in the strand face the same direction; therefore the entire strand has a direction.
6. Which of the following was discovered by Chargaff’s experiment in 1950?
a) base composition
b) base stacking
c) gene morphology
d) chromosome morphology
Explanation: Erwin Chargaff of Columbia University in the year 1950 determined the amounts of each base in various samples of DNA, which is the base composition of samples.
7. Who suggested that DNA composed of three nucleotide strands?
a) Linus Pauling
b) Rosalind Franklin
c) Maurice Wilkins
d) James Watson
Explanation: Linus Carl Pauling was an American chemist, biochemist, peace activist and author. He made an erroneous proposal by suggesting that DNA consists of three nucleotide strands.
8. The helical nature of DNA was revealed by the work of ______________
a) Rosalind Franklin
b) Francis Crick
c) Louis Pasteur
d) Frederick Sanger
Explanation: The helical nature of DNA was revealed in the pattern of spots produced by Rosalind Franklin’s X-ray diffraction image.
9. The phosphate molecules present on the DNA strand give it a large positive charge.
Explanation: The phosphate groups give the DNA molecule a large negative charge. The sugar phosphate bond of each strand is located on the outside of the molecule with two sets of bases projecting towards the center.
10. Which kinds of forces stabilize the DNA structure?
a) hydrophilic, covalent
b) hydrophobic, covalent
c) hydrophobic, van der Waals
d) hydrophilic, van der Waals
Explanation: The bases occupy planes that are perpendicular to the long axis of the molecule and are stacked one on top of the other. The hydrophobic interactions and van der Waals forces between the bases stabilize the entire DNA molecule.
11. What is the width of the DNA double helix?
a) 1 nm
b) 2 nm
c) 3 nm
d) 4 nm
Explanation: The distance from the phosphorus atom of the backbone to the center of the axis of molecule is 1 nanometer (1 nm = 10-9m). The entire width of the double helix is 2 nm.
12. Proteins can interact with a DNA molecule by ____________________
a) fitting into the grooves
b) interacting with the base pairs
c) hydrophilic interactions
d) covalent linkages
Explanation: Proteins have domains that fit into major and minor grooves of the DNA molecule. A protein interacting with the DNA in this way can read the sequence of nucleotides without having to separate the strands.
13. The supercoiled state of DNA was first discovered in the year __________
Explanation: In the year 1963, Jerome Vinograd along with his colleagues at California Institute of Technology was able to discern the DNA supercoiling, following the centrifugation different DNA samples.
14. Supercoiled DNA is more compact than its relaxed counterpart and therefore __________
a) has lower pH value
b) sediments faster
c) sediments slower
d) denatures quickly
Explanation: Supercoiled DNA is the molecule twisted upon itself. It is more compact than the relaxed counterpart and occupies lesser volume. Consequently the supercoiled DNA moves rapidly in response to centrifugal or electric fields.
15. Which of the following is used to visualize DNA molecules in a gel?
a) ethidium bromide
b) methylene blue
d) bromophenol blue
Explanation: In the technique of gel electrophoresis, to view DNA molecules on a gel ethidium bromide is used. EtBr is a fluorescent intercalating agent that inserts itself into the double helix.
Sanfoundry Global Education & Learning Series – Cell Biology.
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